1. Field of the Invention
This invention relates to a portable vibrating massage device, and more particularly, to a portable vibrating device having controls for adjusting the frequency and sequential pulse timing of vibrations.
2. Background Information
On a world-wide basis, a number of pain-control benefits have been associated with the application of localized pressure and vibrations to various parts of the human body. In some instances headaches can be reduced by applying vibration to various locations on the head, and wrist pain may be helped by applying vibration to certain areas of the wrist. A maximum benefit occurs when such pressure and vibrations are applied to particular pressure points, on the surface of the human body. For example, vibration may be directed at nerve endings under the skin.
Vibration may achieve pain control in some instances by tending to overwhelm the sensory system, reducing the ability of other messages, resulting from painful stimuli, to pass through the system. A theory which may further explain the benefits of vibration is the gate control theory of pain, which is discussed by Ronald Melzack and Patrick D. Wall in the Nov. 19, 1965 issue of Science Magazine, Volume 150, Number 3699, pages 971-979. This theory proposes that the substantia gelatinosa, which consists of small, densely packed cells forming a functional unit extending the length of the spinal column forms a gate control system modulating afferent patterns from stimuli before they influence the central transmission (T) cells. Thus, the substantia gelatinosa acts as a gate control system modulating the synaptic transmission of nerve impulses from peripheral nerves to central cells. According to this theory, three features which are important to the afferent input of impulses from a painful stimulus (i.e. to the process of bringing such impulses toward a nerve center) are the ongoing activity preceding the stimulus, the stimulus-evoked activity, and the relative balance of activity in large versus small nerve fibers.
Melzack and Wall describe a scenario in which the spinal cord is continually bombarded by incoming nerve stimuli, even in the absence of obvious stimulation, with this ongoing activity being carried predominantly by small nerve fibers, which adapt slowly, as the gate is held in a relatively open position. If a gentle pressure stimulus is applied suddenly to the skin, the afferent volley of impulses contains large-fiber impulses, which fire the T cells, and which partially close the presynaptic gate, shortening the barrage of impulses generated by the T cells. If the intensity of the stimulus is increased, more receptor-fiber units are recruited, and the firing frequency of active units is increased, bringing about a situation in which the large-fiber and small-fiber inputs tend to counteract each other, as the output of the T cells rises slowly. If stimulation is prolonged, the large fibers begin to adapt, producing a relative increase in small-fiber activity, as the gate is opened further, so that the output of the T cells rises more steeply. However, if the large-fiber steady background activity is artificially raised at this time by vibration or scratching, in a maneuver that overcomes the tendency of large fibers to adapt, the output of the cells decreases.
Melzack and Wall further suggest that there is a temporal and spatial summation, or integration, of the arriving barrage of impulses by the T cells, with the signal triggering the action system responsible for pain experience and response occurring when the output of T cells reaches or exceeds a critical level. While vibration activates fibers of all diameters, it activates a larger proportion of A fibers, which tend to adapt during constant stimulation. While vibration sets the gate in a more close position, the same impulses which set the gate bombard the T cells, summating, for example, with impulses produced by a painful stimulation. Certain behavioral observation indicates that vibration reduces low-intensity pain but enhances high intensity pain.
Since both the different types of pain stimuli, and the various physiological responses to pain stimuli are so varied, any attempt to alleviate pain through the use of vibration should be carried out with equipment having the greatest flexibility in developing different types of vibrations, and in applying these vibrations to the human body. For example, such equipment should provide a means for varying the intensity of vibrations, by varying both the frequency and amplitude of vibrations. Because of the temporal summation effect described by Melzack and Wall, such equipment should have a capability to produce a sequence of vibration pulses, each of which terminates before the pain enhancing effect of summation overcomes the benefits obtained by closing the "gate." Since the benefits of a pain control device using vibration are determined most effectively by the user of the device, controls should be provided on the device to allow the efficient variation of the vibration pattern produced. What is particularly needed is the incorporation of this kind of flexibility into a device which is equipped to maintain suitable contact with the body as it is carried around in use.
One method which has been used to induce vibration, in small devices not used for pain control, is the rotation of a small direct-current motor having an eccentric weight attached to its shaft. Such a motor can be easily driven by means of a small battery. This method has been used, for example, in a pager having a capability of alerting its user that a message has been received by vibrating instead of by producing an audible signal.